2.Emits a large amount of light per x-ray absorption; called conversion efficiency (CE)

3.Light emitted must match the sensitivity of the x-ray film; called spectral matching

4.Fluoresce strongly with little afterglow (phosphorescence)

Screen / Film Combinations

•Designed to compliment each other to produce a quality image

–Intensifying screens manufactured to emit a certain wavelength of light require films to have enhanced sensitivity to the same wavelength

Characteristics of film/screen combinations

•The two important characteristics are speed and resolution

–The speed of an imaging system in inversely proportional to the dose

•As the speed of a system increases the dose required to obtain the desired optical density decreases

–The term “relative speed” (RS) is assigned to film/screen combinations

•RS of 200 is a slower system when compared to a system having a RS of 400

Relative Speed

•When changing from one imaging system to another, the speeds of the two imaging systems must be considered to ensure proper selection of exposure factors

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Resolution

•The ability of an imaging system to demonstrate detail varies on its purpose

–Mammography demands the visualization of fine structure versus abdominal radiography which does not require as detailed imaging

•Also described as recorded detail or sharpness

•Measured as line pairs per millimeter (lp/mm), line spread function (LSP), and modulation transfer function (MTF) (Note, we will study these concept further in Unit 4 – Analyze Image for Quality and Diagnostic Purposes)

•Under ideal conditions the naked eye can resolve ~ 10 to 20 lp/mm

–Direct exposure (non-screen) film = 100 lp/mm

–Detail screens = 15 lp/mm

–High-speed screens = 7 lp/mm

•Inverse relationship between RS and resolution

–As the speed of the imaging system increases the resolution decreases